It is well known in the photographic art to use blue colored polyester support, in particular polyethylene terephthalate (PET) containing 1,4-dianilino anthraquinone pigments, as a base support for radiographic recording elements. In general, these imaging films are spectrally sensitized to green light and undergo wet processing after X-Ray exposure to generate the silver image and remove residual colored materials contained within the film, such as sensitizing and filter (antihalation) dyes. The use of this type of blue support for radiographic film applications serves a psychometric purpose, in that radiologists are accustomed to viewing x-ray images with that background blue tone, and base their diagnoses on examination of films which have that blue tone. The pigment which imparts the blue color to the film serves no other purpose (such as spectral sensitization or antihalation) in such applications.
In recent years, imaging films which rely on the use of lasers, particularly solid state diode lasers, as the exposure source have been developed, which have required the use of antihalation and sensitizing dyes that absorb in the same region as the exposure device. Generally, these dyes do not impart a blue hue to the film as radiologists have come to expect, but as in more traditional radiological imaging films, this is of little consequence as long as the film undergoes subsequent wet processing steps that remove these residual colored materials. The limitation of this becomes obvious in trying to develop films based around so-called dry silver technology. These films utilize a light sensitive silver halide in catalytic proximity to a light insensitive, reducible silver source, along with a reducing agent for the silver source. The silver image is produced upon heating the element after exposure, without the need for wet processing. Residual sensitizing and antihalation dyes impart undesirable color to these films, making the images unacceptable from the colorimetric viewpoint of the radiologist, despite the fact that the images are acceptable in terms of other criteria, such as sharpness, D.sub.min, contrast, etc.
It is known in the art that dyes can be incorporated into photosensitive materials to improve the color tone of developed silver of emulsion grains. The color tone of a developed silver image can often appear yellowish, particularly when using tabular grain emulsions, due to the yellow light produced by the scattering of blue light by the developed silver. Several variations of this technology have been disclosed in the art.
U.S. Pat. No. 4,847,149 discloses the use of fluorescent brightening agents to improve the color tone of a silver image in a sensitive material using tabular grain silver halide emulsions.
U.S. Pat. No. 4,818,675 discloses a technique for improving the blackness of a silver image by incorporation of a dye having maximum absorption between 520-580 nm in a sensitive material which uses tabular silver halide grains.
U.S. Pat. No. 5,213,951 discloses the use of a blue pigment having an absorption between 570-630 nm in a sensitive material comprising tabular silver halide grains to mask residual dye stain in the film.
U.S. Pat. No. 5,262,286 discloses the use of a tinting pigment in a sensitive reflection print material to compensate for the perceived yellowness of the sensitized material.
Various color toning agents which modify the color of the silver image of photothermographic emulsions to give a black or blue-black image are also well known in the art as exemplified by U.S. Pat. Nos. 4,123,282, 3,994,732, 3,846,136, and 4,021,249.
In all these cases, the coloring agent is added to mask dye stain or alter the perceived reflective tone of the silver image to make it colder (bluer). It would be desirable to have a photosensitive material, particularly a photothermographic material, which exhibited improved image tone with regard to the perceived background color, such that it matches the blue background color that radiologists prefer, and have come to expect in radiological films.